IMAP4 is a mail protocol that allows users to be disconnected from the main messaging system and still be able to process mail. Users can store messages on a local machine or on a server.
IMAP has distinct advantages over POP because it allows you manage multiple folders on the server. Mail can be accessed from different machines, as the mail is hosted on the server (unlike POP which deletes mail from the server after being accessed) and allows the user to just download message headers and envelope information, until the user selects the email to download. This is useful when operating over slow speed dial-up connections.
IMAP4 can break up and download specific parts of a multi-part email message (MIME). This means that instead of having to wait for an email with attachments to download, you can select only the text portion to download, and leave the attachments on the server.
IMAP4 allows you to have server hosted folders and subfolders.
Click here for details about how to configure the IMAP service.